This domain is found in a number of bacterial chitinases and similar viral proteins. It is organised into a fibronectin III module domain-like fold, comprising only beta strands. Its function is not known, but it may be involved in interaction with the enzyme substrate, chitin [1,2]. It is separated by a hinge region from the catalytic domain (Pfam:PF00704); this hinge region is probably mobile, allowing the N-terminal domain to have different relative positions in solution [1].
PFAM PF08329